A fork is when a blockchain network changes its rules – but there are hard forks and soft forks, and which one happens makes a big difference.
Bitcoin runs on consensus. The decentralised network of miners agrees on the contents of the ledger – the blockchain – and makes sure that no one tampers with it. This alone is an amazing feat, and it enables peer-to-peer money. Previously, electronic cash always needed a trusted third party to keep accounts.
The network relies on the fact that everyone knows and enforces the same rules. But what if those rules need to change? Maybe there’s a security hole that needs patching. Or maybe the platform is getting a major upgrade with new functionality. That’s when you need a fork.
Soft and hard
In the crypto world, a fork is a change in the rules of consensus. But there are two kinds of fork: hard forks and soft forks. Soft forks are back-compatible. That means the network continues running as it was, no matter who has upgraded to the new software. Old and new versions continue to work seamlessly together. But with a hard fork, clients running new and old software are not compatible. They won’t ‘talk’ to each other. This is when you get a blockchain fork – two separate networks, with miners running different software.
Andreas Antonopoulos has described the difference between a hard and soft fork like this: If a vegetarian restaurant decides to add meat to their menu, that’s a hard fork: a change in the rules that is incompatible with their previous approach. But if they add vegan dishes, that’s a soft fork. Vegetarians could still eat there and enjoy the new vegan food, without having to change their existing habits.
A soft fork is far less disruptive to the network, because miners don’t have to upgrade to continue mining (even if it’s desirable for one reason or another). But sometimes a hard fork is necessary, especially if a security vulnerability needs fixing. And, of course, there are times when developers want to split the network with a hard fork. This is what Bitcoin Cash did when it changed the rules of consensus and split from the Bitcoin Core network. It’s also what Bitcoin Cash SV did when it split from Bitcoin Cash.
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